Wednesday, December 31, 2014

CDM 1550 duty cycle

My good friend Tom KJ9P did some testing of the use of Motorola CDM 1550 mobile radios as repeaters. You can use these as repeater receivers or transmitters, but you will need to add a cooling fan. I also recommend not running higher than 50% of the rated power output.

Here's Tom's results:

At idle, and both receivers on, the power consumed is .4 amps.


At Low Power Transmit (8 Watts out) the power consumed is 2.6 amps.


At High Power Transmit (22 Watts out) the power consumed is 4.0 amps.


Temperature rise after one minute of keydown on either low or high power is two degrees with fan cooling 100% of the time.

Wednesday, December 3, 2014

McLean County Illinois DSTAR Coverage

I've found that there are two site options when you're building a repeater...find a really tall structure (tall relative to terrain) or put up multiple sites. We've not had much luck finding a really tall structure in Bloomington, IL for our DSTAR system. So we've got two sites active right at my farm in Heyworth and one in North Normal at KJ9P's QTH. By having two sites active, we've filled in most of the geography for the county. There are still some spots that are aren't going to be able to use a handheld from downtown Bloomington. But hey, we're amateurs and we're learning!

Tuesday, December 2, 2014

DSTAR Commands - A Quick Guide

Reading through all of the DSTAR documentation can get a little crazy. Here is a quick reference on linking commands. 

There are four callsign settings on your radio that you can adjust. They are:

MYCALL: Should always be your callsign, like KG9DW

RPT1: Should be the callsign of the repeater module you're connecting to, with the callsign in positions 1 through 6, a space in position 7, and then the module letter. The module letter is B for UHF or C for VHF; So for Heyworth, that would be KD9AKF B. For Normal, that would be WX9WX  B. Notice that because Normal is a 2x2 call, you have two spaces between the X and the B.

RPT2: If you want to use the gateway (not have your traffic only stay local) then this should be set to the same as RPT1 but the module letter (position 8) should be G. So for Heyworth KD9AKF G or for Normal WX9WX  G. Almost always, you'll want to use the Gateway.

URCALL: This is where you put the command you want the repeater to do.

The fun is with URCALL:

CQCQCQ means let your voice be heard everywhere.

E in the 8th position does an echotest - it repeats your audio back to you.

I in the 8th position tells you if the repeater is linked, and what it is linked to.

U in the 8th position unlinks the repeater if it is linked.

L in the 8th position, with a callsign+module or reflector name in positions 1-7 links the repeater. For example, REF001BL links the repeater to reflector 001B. KC9YFXBL links the repeater to the Decatur repeater. 

*** IMPORANT *** : After you use the E, I, U, or L commands, switch back to CQCQCQ to carry on a QSO! If you keep sending a link command, the repeater will keep linking or relinking and no one will hear your call!

A typical use of the repeater to link to reflector 001B would be:

1. Key up with I to see if the repeater is linked
2. To link, key up with REF001BL
3. Switch to CQCQCQ and begin your call or QSO

A typical use of the repeater to link to Decatur would be:

1. Key up with I to see if the repeater is linked
2. To link, key up with KC9YFXBL
3. Switch to CQCQCQ and begin your call or QSO

Feel free to leave the repeater linked...linking invites more QSOs and more traffic! If you are working on your radio or want to just play, unlink the repeater so that only local users hear your testing.

Whew, that's a lot to understand. Not to try to confuse you, but you can use DTMF codes with our non-ICOM repeaters as well. This allows you to link without having to program up your URCALL. This is useful when you want to link to an odd-ball reflector. For information on those commands, visit:

Above all, have fun, and let me know if you need help!

73, Michael

Monday, December 1, 2014

Cabling a DVRPTR board to a CDM1550 for a DSTAR Repeater

I'm playing with a couple of CDM1550 radios to be used as another DSTAR repeater. I've had pretty good luck with the Kenwood TKR-820, although it can be very finicky. You're using early 80's technology with the Kenwood, where you're using 21st century tech with the CDMs.

Here's how I've cabled my board to two CDM1550 Motorola UHF radios:

CDM1550 (T=transmitter, R=Receiver), purpose, DVRPTR
T5, tx mod in, 1 red
R11, rx dis out, 4 black
T3, PTT, 3 grey
T7 and R7, grnd, 2 green
R15, cos/rus, 6 blue
T10/R10, ignition sense, connect to 12V

You'll also have to do some programming in the CDM:
1. Turn on the flat tx audio when using the external ptt line
2. Set accessory port 3 to be PTT when low
3. Set the tx power low (I'm using 10 watts, and keyed down for 20 minutes wasn't too hot on the heatsink)
4. Set the transmitter timeout to 180 seconds for each channel
5. Set the on/off to be the front panel button and also the ignition sense wire

You need to take pin 10 to 12V so that if the power supply goes off, the radios will power back on by themselves. Without this pin connected, a power failure will cause the radios to stay off when the power returns!

A big advantage of the CDMs is the ease at programming the frequencies. With the right software, it is a breeze. The problem, the software isn't cheap. Luckily I have the software available from my work at the fire station. 

For my setup, I put both the transmit and receive frequencies in both radios as simplex channels. That way, if my transmitter finals go bad, I can swap the accessory plugs, change the selected frequency on each radio, and be back on the air. Of course, if the finals go out, it likely is because of an antenna system failure or because I ran the transmitter too hard!

UPDATE: Here's a pdf version of the wiring diagram that Tom KJ9P created. Thanks Tom!